I have installed a marten protection, a combined system with ultrasonic and high voltage. The power supply is directly via battery plus and battery minus. There is no connection to terminal 15. Whether the vehicle is driving or parking, is determined by the battery voltage. Above 13,x V, the integrated control unit assumes that the engine is running and shuts off the system. So far all this is clear. Now there is an additional bonnet contact, the system b The switch is connected only to a single cable, which leads to 300 V voltage, i.e. the normal operating voltage of the electrical contacts. According to the installation instructions, the switch itself must be well connected to ground by means of its fastening screw. How does this work? The switch cannot do more than to establish or disconnect the connection to the ground. A connection between Mass and +300 V would be a short circuit.